458
FXUS63 KAPX 191607
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1107 AM EST Sun Jan 19 2025

.KEY MESSAGES...

- Cold Temperatures and Wind Chills through Tuesday Night...

- Lake effect Snow through at least Tuesday night...

&&

.UPDATE...
Issued at 1103 AM EST Sun Jan 19 2025

Inherited forecast remains in excellent shape with only cosmetic
changes warranted to account for real-time observations. Lake
snows continue to impact our traditional snow belt
locations...and will continue to do so right through tonight
(and beyond). Loss of dendritic growth layer now well evident by
small flake size...which are inefficient in accumulating by
more than efficient at reducing visibilities. Will likely need
additional headlines with the afternoon forecast release to
account for increasing travel difficulties. Quick perusal of
temperatures also shows potential for the need for cold weather
headlines by later tonight. Will continue to evaluate.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 339 AM EST Sun Jan 19 2025

     Continued cold with lake effect snow showers...

Arctic airmass continues to spill into much of the US early this
morning...including the entire Great Lakes region. NW flow lake
effect snow showers continue to stream into our typical snowbelt
regions. Overall snowfall has been generally light thanks to very
cold temps...leading to small snowflake size which are efficient at
reducing vsbys but not at stacking up/accumulating. Temps continue
to drop thru the teens toward early morning lows in the single
digits above zero.

Strong CAA will continue today and tonight. 850 mb temps across our
CWA will drop several degrees from the negative 20s (C) this morning
to the negative mid to upper 20s (C) this afternoon and tonight.
Inversion heights will gradually rise just a bit over the next 24
hours...lifting from around 5-6 kft this morning to 7-8 kft by
tonight. Upper level trough axis will swing thru Michigan this
evening...with deep cyclonic flow holding over our area thru tonight
(at least). Near term models show sharp lake aggregate troughing
holding over Upper Michigan and Lake Superior for the next 24
hours...providing continued enhanced low level convergence across
this area. Maintenance of arctic airmass/temps across our area will
keep snowflake size small...but some lift in inversion heights
should give snowfall amounts a bit of a boost thru tonight.

Heaviest and most persistent snowfall will remain focused around the
Whitefish Bay area today and tonight...where new snow amounts of 2
to 3 inches are expected today...with an additional 2 to 4 inches
expected tonight. Will therefore extend the ongoing Winter Wx
Advisory for Western Chippewa county thru tonight. Rest of our
snowbelt areas should see a general 1 to 3 inches of new snow today
and another 1 to 3 inches tonight...with some locally higher amounts
possible. These amounts generally fall just below advisory criteria
and will therefore hold off on issuing any headlines for now.

Very cold temps will remain in place thru tonight...but wind chills/
apparent temp values will remain above any headline criteria. High
temps today will only reach into the teens...with overnight lows
dropping into the single digits above and below zero.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 339 AM EST Sun Jan 19 2025

PATTERN SYNOPSIS/FORECAST:

Polar flow continues to overtake the central continent...behind a
reinforcing upper trough axis dropping into the Great lakes as of
4z. Cold advection plentiful...with 850mb temps of -25 to -30C just
to our north over Canada...resulting in strengthening of lake
aggregate troughing (and continuation of lake effect snow) over the
Upper Great Lakes. Friday`s cold front and related warmth only a
memory...as it continues to chug toward the East Coast.
Upstream...ridge axis remains steadfast over Alaska, though some
subtle warm advection starting to show up over the western
US...despite a niblet making its way through the flow over British
Columbia/Idaho. Anomalous 1044mb cold surface high oozing into the
northern Plains...accompanied by sub-zero surface temps and surface
dewpoints south of -25F.

Trough axis to continue to pivot through early today, keeping the
cold air flowing southward into the Midwest...and keeping the lake
aggregate trough in play. Flow turns a bit more zonal Monday as a
niblet of PV digs into the Upper Midwest...resulting in a more zonal
lake aggregate trough, as surface high pressure and attendant cold
air ooze down around the Great Lakes into the OH Valley. Trough axis
finally gets punted out of the region going into Tuesday night and
Wednesday, though cold air will linger into Wednesday morning before
eastward-building shortwave ridge and attendant strengthening
southwesterly flow finally bring moderation to our region after a
few days of very cold temps. Pattern looks to turn a little more
zonal over the bulk of the US toward the end of the period, with
eastern Pacific pattern appearing to breakdown to some degree. While
things remain unclear for the latter part of the period,
particularly noting that guidance is just now starting to get a
better handle on things for late week...think the current idea could
set up a baroclinic zone somewhere across the US as we get into next
weekend, which could certainly bear watching going forward if this
idea continues to hang on.


Primary Forecast Concerns:

Cold Temperatures...Sub-zero daytime highs possible Monday, and
perhaps even Tuesday, as the core of the coldest air passes around
the region...based on pattern recognition from other cold events
(e.g., Feb 19 2015). However...with cloud cover likely due to lake
convection...current suspicion is that we will float around or just
above zero over most of the area for both Monday and Tuesday,
depending on how cold we get tonight and Monday night (as the cloud
cover could also lend to a much smaller diurnal swing). Coldest
temps seem likely for the EUP particularly with the potential for
drainage flow out of Canada...though the sticky wicket will be the
focused convergence band/lake aggregate trough and just how much it
will be able to remain clear over Chippewa county in particular,
which should be more favored for convergence and subsequent lake
convection with time as the shortwave trough moves through and turns
the lake aggregate trough a bit more zonal...shifting it back toward
the Soo from closer to Tahquamenon Falls/Newberry. Think we will
have to keep an eye on NE Lower, too, where there is a greater
potential for drier, less-modified air as the cold air horseshoes
around the Upper Great Lakes/lake aggregate trough...as well as more
clearing away from the lakes, though unclear if we will decouple
enough to completely bottom out.

Wind chills through the period very likely to approach critical
thresholds of -15F across parts of northern Lower, esp south of M-72
per the last part of the paragraph above, where winds should also be
a touch higher, though not by much (4-7kts compared to less than 2-
5kts across the EUP under the lake aggregate trough). For the
EUP...any wind at all could very well result in reaching or
exceeding critical -20F thresholds.

Lake effect snow...Still looking at a prolonged period of lake
effect snows...initially focused more NW Monday...but shifting more
WNW late in the day, generally remaining westerly into Tuesday and
Tuesday night (perhaps turning more WSW going into Wednesday
morning). Primary focus will be the lake aggregate trough/enhanced
fgen areas across the EUP/SE Lake Superior, which has potential to
shift back to the east with time Monday as the colder air oozes
around to the south and flow becomes more zonal overall...ultimately
looking to shift offshore into Lake Superior going into Tuesday
night and Wednesday as flow turns more WSW/SW. The period of
greatest accumulations should be Monday into Monday night when
inversion heights will be highest and moisture deepest over the EUP
and northern Lower (esp north of M-72). With thermal profiles almost
entirely colder than the DGZ, expecting fine snowflakes that will
not accumulate as efficiently as the fluffier stuff we`ve been used
to...though smaller flakes come with their own set of impacts, as
they tend to be easier to blow/drift and reduce visibility.
Still...a general 2-4 inches likely during the day Monday in the
snowbelts, even with winds shifting from NW to more W with time
(which should also put a damper on snowfall totals), and perhaps
again Monday night...with any pivot points (such as western Chippewa
and perhaps parts of Antrim/Charlevoix county) at a greater risk to
see localized higher totals of 4-6+ inches through Tuesday night.
Aside from visibility reductions and blowing/drifting potential with
the finer snowflakes (though winds not expected to be terribly
dramatic through the period)...another potential impact with
snowfall during this period is that regular old sodium chloride salt
should be at or below the limit of its effectiveness, given the
expected single digit temps. Interested parties may wish to do
research on effectiveness of alternate salts/snow-melts at such
cold temps (I do not have the time right now and don`t remember
off the top of my head).

Looking ahead...will need to keep an eye on warm advection snow
potential Wednesday ahead of the next bit of energy approaching the
region, as there may very well be a decent shot at putting an
isothermal layer in the DGZ. Could be looking at some decent lake
enhancement potential on SW flow as well. With potential for a
couple different niblets to meander their way through the
Midwest...will have to monitor this for chances for better
widespread/synoptic snow potential at times going into the latter
half of the week.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 600 AM EST Sun Jan 19 2025

NW flow lake effect snow showers will continue to stream into
our typical snowbelt regions today and tonight. Prevailing
conditions will remain low VFR/MVFR...temporarily dropping to
IFR within some of the more persistent/heavier snow showers.
Surface winds will remain mostly from the NW AOB 10 kts.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 5 AM EST Monday for MIZ086.
MARINE...None.

&&

$$

UPDATE...MSB
SHORT TERM...MLR
LONG TERM...FEF
AVIATION...MLR